One-dimensional ribbon-like structures embedded in single-layer graphene on Ni(100)

Lateral confinement is one of the prominent strategies for tailoring the electronic properties of 2D materials. The most typical example of one-dimensional (1D) quantum confinement is the graphene nanoribbon (GNR), whose edges forces electrons to be trapped in a nanometer-wide stripe, thus modifying the electronic state from semimetal (2D graphene) to semiconductor. Nonetheless, physical edges are not the only factor leading to 1D electronic states. In this work, researchers have demonstrated that 1D ribbon-like structures with zigzag edges – called “pseudo-ribbons”, GPRs – exhibit many of the electronic properties found in GNRs even if they are embedded in a continuous single-layer graphene sheet. The characterization of these stripes has been accomplished by a comprehensive approach combining Scanning Tunneling Microscopy and Spectroscopy findings, Spectroscopic PhotoEmission and Low Energy Electron Microscopy (SPELEEM) measurements carried on at the Nanospectroscopy beamline of Elettra and ab initio simulations.
The formation of 1D structures is based on the thermally-controlled segregation of carbon atoms at the interface between graphene and a Ni(100) substrate. Such segregation is patterned by the natural 1D moiré occurring between the hexagonal 2D lattice vector of graphene and the squared 2D lattice vector of the Ni(100) surface, and modifies locally the electronic properties of graphene by removing its interaction with the Ni atoms. As a result, long, parallel lifted graphene stripes form, reaching several hundreds of nm in length while maintaining the width quantized by the 1D moiré - about 1.4 nm (see homepage figure). The mechanism is sketched in the atomic model of the surface in side view presented in Figure 1a, together with an atomically-resolved STM topographic image of a single GPR. The presence of nickel carbide underneath is proved by the C 1s photoemission peak extracted from a stack of X-ray PEEM images (Figure 1b). The peak consists of two main components, associated with interacting graphene on clean Ni(100) (blue) and noninteracting graphene (green), and of two less intense components at lower binding energy, assigned to isolated C atoms dissolved into Ni bulk (cyan) and nickel carbide at the interface (purple). Annealing above the carbide decomposition temperature demonstrates that the noninteracting component and the interfacial nickel carbide are linked, as they appear and disappear together when the temperature changes.
DFT calculations assessed the electronic structure of GPRs. Figure 1c shows the projected density of states calculated for C atoms placed on top (left) and at the edges (right) of the GPR and resolved over the k-space. It is clear that in the center the pseudo-ribbon the graphene π-bands are restored, while on the edges localized electronic states with flat dispersion around Γappear. These findings strongly support the picture that electrons in GPRs are subject to lateral confinement and present edge states as in the case of GNR with zigzag edges, even if the 1D structure is embedded in a continuous 2D material.

 figure 1

Figure 1.  1) Top, side view of the model structure of pristine graphene/Ni(100) surface and of a single GPR with a surface nickel carbide (in red) underneath. Diluted carbon atoms are shown in yellow. Bottom, atomically resolved STM topographic image of a single GPR embedded in a graphene sheet. The hexagonal texture of graphene is superposed to guide the eye. STM parameters: bias -0.3 V, tunneling current 0.5 nA. 2) X-ray Photoemission Spectra of C 1s line of the surface. For explanation see text. 3) calculated band structure of the GPR projected over a single zigzag row of C atoms placed on the center (left) and on the edge (right). The atomic model on top highlights the C atoms involved in the projection.

The formation of 1D structures naturally aligned with the substrate on a mesoscopic scale offers the rare possibility to investigate the electronic band dispersion of GPRs by probing with SPELEEM the angular distribution of electrons photoemitted from a few-micrometers wide region. One angular pattern with inverted colors is presented on the right of the homepage figure. Here, band features reminiscent of graphene Dirac cones are clearly visible at the K points, with a pronounced elongation in the horizontal axis. Such distortion has been rationalized as an effect of 1D lateral confinement on the Dirac cones. Then, the band structure of the system with aligned GPRs was extracted. Such analysis shows direct evidence that the electronic states of GPR suffer a depletion compatible with the opening of a bandgap, i.e. with the induction of a semiconducting state by lateral confinement.
In conclusion, this system constitutes a topical example in which 1D electron states are present within a continuous 2D film and looks promising in the exploitation of 1D characteristics. GPRs are expected to behave like nanowires with enhanced charge/spin transport properties and can be used to create model devices at the mesoscopic scale, as well as a template to build aligned 1D heterostructures via e.g. deposition of metals (nanowires) or molecules (1D frameworks).


This research was conducted by the following research team:

Alessandro Sala1,2, Zhiyu Zou1, Virginia Carnevali2, Mirco Panighel1, Francesca Genuzio3, Tevfik O. Menteş3, Andrea Locatelli3, Cinzia Cepek1, Maria Peressi2, Giovanni Comelli1,2, Cristina Africh1


Istituto Officina dei Materiali, CNR, Trieste, Italy
Dipartimento di Fisica, University of Trieste, Italy
Elettra Sincrotrone Trieste S.C.p.A., Trieste, Italy

Contact persons:

Alessandro Sala, e-mail:



Alessandro Sala, Zhiyu Zou, Virginia Carnevali, Mirco Panighel, Francesca Genuzio, Tevfik O. Menteş, Andrea Locatelli, Cinzia Cepek, Maria Peressi, Giovanni Comelli, Cristina Africh, “Quantum Confinement in Aligned Zigzag “Pseudo-Ribbons” Embedded in Graphene on Ni(100)”, Adv. Funct. Mater 13, 2105844 (2021), DOI: 10.1002/adfm.202105844

Last Updated on Monday, 10 January 2022 15:42